The use of radio communication networks is rapidly becoming a part of the daily life for more and more people around the globe. For instance, the GSM (Global System for Mobile Communications) networks offer a variety of functions. Generally, radio communication systems based on such networks use radio signals transmitted by a base station in the downlink over the traffic and control channels are received by mobile or portable radio communication terminals, each of which have at least one antenna. Historically, portable terminals have employed a number of different types of antennas to receive and transmit signals over the air interface. In addition, mobile terminal manufacturers encounter a constant demand for smaller and smaller terminals. This demand for miniaturization is combined with a desire for additional functionality, such as having the ability to use the terminal at different frequency bands, e.g., of different cellular systems, so that a user of the mobile terminal may use a single, small radio communication terminal in different parts of the world having cellular networks operating according to different standards at different frequencies.
Further, it is commercially desirable to offer portable terminals that are capable of operating in widely different frequency bands, e.g., bands located in the 800 MHz, 900 MHz, 1800 MHz, 1900 MHz and 2.1 GHz regions. Accordingly, antennas, which provide adequate gain and bandwidth in a plurality of these frequency bands, are employed in portable terminals.
The general desire today is to have an antenna, which is positioned inside the housing of a mobile communication terminal. Several attempts have been made to create such antennas.
For instance, U.S. Pat. No. 6,650,294 of Ying et. al., discloses broadband multi-resonant antennas that utilize a capacitive coupling between multiple conductive plates for compact antenna applications. The number and design of conductive plates is set to achieve the desired bandwidth. One of the antennas discloses by Ying is designed for four resonant frequencies and includes three L shaped legs, each including a micro-strip conductive plate and connection pin, with configurations approximately parallel to one another, wherein the center L shaped leg is a feed patch with a feed pin connected to a transmitter, receiver, or transceiver. The upper L shaped leg is a dual band main patch and ground pin. The dual band main patch has two different branches with different lengths and areas to handle three of four desired resonant frequencies. The lower L shaped leg is a parasitic high band patch and ground pin designed to handle one of the two higher desired resonant frequencies. Ying has proposed an antenna that uses a capacitive feed structure and capacitive coupling along the low-band branch in order to achieve improved bandwidth at the low-band. However, the multi-layer design with capacitive coupling proposed by Ying has somewhat reduced performance in the low-bands and does not have sufficient bandwidth in the high-bands, for instance to achieve a suitable digital cellular service (DCS)/personal communication service (PCS)/universal mobile telecommunications system (UMTS) performance.
Another example for an antenna is disclosed in WO2005/057722, by Antenova Limited, wherein a high-dielectric ceramic pellet is used as part of a feed structure. More precisely, the antenna structure disclosed in WO2005/057722 has a dielectric pellet and a dielectric substrate with upper and lower surfaces and a ground plane. The dielectric pellet is provided with a conductive direct feed structure. Further, a radiating antenna component is additionally provided and arranged, so as to be excited by the dielectric pellet. This design may in particular achieve broad bandwidth in the high-band, especially when using matching components. However, an antenna structure as proposed by WO2005/057722 may have reduced gain. Additionally, the cost of implementation can be prohibitive due to the elevated costs of the specialized ceramic materials, as specific dielectric pellets made of a highly specialized ceramic material are needed.
Hence, an improved multi-band radio antenna device having a wide high-bandwidth would be advantageous. In particular a multi-band radio antenna device allowing for increased efficiency with regard to, e.g., size, cost, bandwidth, design flexibility and/or radiation efficiency of the multi-band radio antenna device would be advantageous. It is desirable to achieve an antenna supporting at least a single low-band and a wide range of multiple high-bands.
More specifically, an antenna with very broad high-band would be advantageous, which is both small and has good performance also in a low frequency band, such as the 900 MHz GSM band. The high-band performance is desired to be good in several higher frequency bands, such as the 1800 MHz GSM or DCS band, the 1900 MHz GSM or PCS band, and the 2.1 GHz UMTS band.
Hence, an improved multi-band antenna would be advantageous, and in particular a multi-band antenna allowing for increased performance, flexibility, or cost-effectiveness, would be advantageous.